Stoker damper control



Oct. 2, 1945. H. a MALONE I 2,335,822

' STOKER DAMPER CONTROL Fiied Aug. 3, 1940 mom I Hmms'r' E; alone ATTORNEY.

Patented Oct. 2, 1945 STOKER DAMPER CONTROL Homer E. Malone, Milwaukee, Wis., assignor to Perfex Corporation, Milwaukee, Wis., a corporation of 'Wisconsin Application August 3, 1940, Serial No. 350,396

20 Claims.

This invention relates in general to damper control means, but more particularly to an improved air damper control for stoker operated furnaces, and the principal object of the invention is to provide a novel automatic air damper control means for delaying the initial admission of forced combustion air to the burning fuel bed of a furnace.

In the ordinary operation of furnaces equipped with stoker fuel feeding means it is customary to provide a blower or fan operated by the stoker motor to deliver forced combustion air to the burning fuel bed on the furnace retort. This forced air is delivered simultaneously with the feeding of the fuel to the retort so that good combustion of the fuel will take place. In domestic installations the stokerapparatus is usually controlled automatically by a temperature responsive device such as a room thermostat which starts the stoker when the room temperature reaches a predetermined value. There is also usually provided an interval timer device for starting the stoker apparatus at predetermined intervals independently of the room thermostat so that the fire upon the fuel bed will be maintained alive during long periods when the room thermostat does not call for heat, such as occurs in mild weather.

During continued operation of the fuel feeding mechanism to feed coal upon the furnace r'etort, the portion of the fuel bed throu h which the combustion air is forced is maintained ata fairly constant depth and density when the rate of fuel feeding is substantially equal to the rate of burning. However, during an off or standby period of the stoker the fuel upon the retort continues to burn as a result of some natural draft, and the thickness of the fuel bed consequently may be substantially reduced before the next operation of the stoker occurs. Accordingly, when the stoker is again started the initial blast of forced combustion air from the fan will blow the fly" ash from the thin fuel bed before the bed can be built up with fresh coal. Blow holes may also occur in the thin' fuel bed through which the forced air will rush and out the furnace and the resultant deposit of the same greatly reduces the eiiiciency of the heating plant, causes annoyance by settling about the premises, and is a factor concerning the health of a community.

It is an object of the invention to provide an air damper for a stoker air duct which is automatically controlled in a manner to retard its initial opening movement to delay the delivery of the full blast of air from the air fan to the fuel bed until a proper amount of coal has been fed upon the fire bed, and to gradually permit opening of the damper to its full open position and enable maximum air volume to pass only after the stoker has run for a certain period. This delay in the delivery of the full blast of air enables fresh coal to be fed to the thin fuel bed on top of the ashes, preventing the diffusion of fly ash through the furnace and causing the ash to become substantially fused.

A further object of the invention is to provide a stoker air damper arrangement in which a delayed opening of the damper takes place responsive to the control by the room thermostat, but when-the stoker is controlled by the interval timer to maintain the fire alive, the damper remains in closed position.

Another object is to provide an improved air damper control having electrically controlled thermally actuated means for controllingthe delayed opening of the air damper.

It is a further object to provide means in case the thermal electric actuator is disabled toinsure that the damper is restored to its normal closed position. 1

A further object is to provide a damper control means in which the air damper in its normally closed position will serve as a banking damper and upon initial operation of the air fan a time delay is introduced to delay the opening of the damper after which the damper is arranged free to move unrestrained to any open position dependent upon the air pressure acting upon the damper and therefore the porosity or depth of the fuel bed.

An additional object is to provide an automatic air damper control in which the return of the air damper to its closed or banking" position is delayed when the stoker is stopped, and the damper is held in a partially open or intermediate position for an interval so that the volatile gasses from the fresh fuel on the fire bed are driven off and the passage of smoke back through the stoker apparatus is prevented.

Other objects of the invention are concerned justed; whereby the amount of the temporary partial opening of the damper when the stoker shuts down is rendered adjustable; and whereby the amount of biasing forcetending to restore the damper to closed position is adjustable.

With the foregoing and other objects in view which will become more full apparent as the nature of the invention is understood, the invention consists in the new and novel features of construction, operation and arrangement of.

the parts as will be hereinafter more fully described in the specification, illustrated in the accompanying drawing, and defined in the appended claims. a Y

The invention in one of its preferred forms is illustrated in the draWing in which:

Fig. 1 shows diagrammatically a View of a stoker furnace installation together with the Various control elements and associated electrical wiring therefor;

Fig. 2 is a cross-section top view through the housing showing the damper control device'of the. invention mounted on the side of the air duct of the stoker installation; and

, Fig. 3 is a side elevational view of the control device with the cover removed to show the internal mechanism.

' Referring specifically to Fig. l a conventional domestic: stoker installation is depicted comprising the usual retort 5 for supporting the burningfuel. bed within a furnace not shown, and having a wind box 5 positioned below the retort 5.. The retort '5 is arranged with a series of tuyeres'not. shown, through. which the forced combustion 'air' passes to. the burning fuel from the blower or fan i!) is drivenbythe motor 8 to be adjustable. Also in some stoker installations separate motorsmay be, provided for driving the fuel conveyor screw and the air fan.

r The operating control means for operating the stoker installation includes an electromagnetic relay having a winding I2 adapted when energized'to close a pair. of motor contacts l3 and complete, an operating circuit for the motor 8 from'a suitable source of commercial current fed over a pair of line wires l4 and I5. A transformer it has a primary winding connected across the line wires l4 and I5, and a secondary winding for feeding low voltage operating current for relay winding 52. The primary control for, operating the stoker mechanism may be any type of control means whereby the stoker is automatically operated when the temperature of a boiler or room; drops below a predetermined minimum value, or the steam pressure of a steam boiler is below a desired value. In the preferred form this may comprise a room thermostat such as shown diagrammatically at I! having a set of operating contacts which are adapted to close upon a drop in room temperature to complete an energizing circuit for the relay winding l2. During, long intervals between operations of the room thermostat H such as would occur in mild weather, it is customary to provide some form of interval timer to periodically operate the stoker independent of the room thermostat and thereby maintain the fire alive. This ma take the form of a constantly operating electric motor l8 to which a cam member is coupled for closing a pair of contacts l9 at regular adjustable intervals and for relatively short adjustable periods of time. These contacts l9 are connected in parallel with the contacts of the room thermostat If! and perform the same function in controlling the stoker motor.

Although some variations in the form and number of the controls may be desirable to lit the requirements of different types of stoker installations, the foregoing described apparatus is merely conventional and illustrative of the generally accepted forms. A furnace stoker operating with the foregoing controls will operate in a somewhat satisfactory manner as long as the fuel feed and the forced air passing to the retort.5 are adjusted in the correct. proportions and ratioto provide eflicient combustion conditions in the burning fuel'becl. However upon each initial operation of the stoker motor and. air fan upona thin or porous fuel bed, the fly ashis blown about in the manner pointed out, rendering the operation of the furnace less efficient. The means for obviating this disadvantage and others according to the invention comprises an automatic damper control for delaying temporarily the admission of air to the stoker retort for a time until the possibility of fiy ash diffusion has been passed. This automatic damper control is: indicated generally at 20 and is situated upon the air duct II in a position between the windv box 6 and the air fan It where the device can exercise full control. over the volume of forced air passing to the stoker retort 5. The control device 2!} is connected in a parallel circuit with the stoker motor 8 and therefore is energized each time the stoker is operated. A rheostat 2| is electrically connected in series with the control device for regulating its operation as will be pointed out.

The automatic damper control 20 as shown in detail in Figs. 2 and 3 is enclosed in a metal'housing ,or' casing 22 which is supported against one of the sides of the air duct H by means of several screws 23'. movably secured tothe'housing 22 by screws 25 at opposite ends of the housing. Arranged within the air duct I l' is an air valve or damper 26 shapedin the form of a fiat metal vane which naled inopposite sides of the air. duct H as shown and at one side includes a bearing 'mem- 'ber 29 fastened tothe side of the duct. A sleeve member '30 is securely fastened to the shaft 2! inthe housing 22' by aset screw 3| and carries a crank arm 32 at one end. Crank arm 32 is provided with a'pin 33 at its end to which one end of a link member 34 is pivotally secured.

Arranged Within the casing 22 there is also a latching'member or plate 35of general quadrant shape which is attached to a sleeve 31 which in A suitable cover plate 24 is return is rotatably mounted on a pin 36. The pivot pin 36 is fastened by the nuts 38 to the side of the casing 22 as shown. The lower'end of the latching member 35 is provided with an ear shaped portion which carries a pin 39 to which one end of the link member 34 is pivoted. With the foregoing arrangement the damper 26 is linked with the latching member 35 and both are always moved or rotated together about their pivots 21 and 36 respectively.

Along one edge of the latching member '35 there is arranged a weight or mass 40 which is adjustably secured to the latching member'35 by clamping screw 4|. The purpose of the weight 40 is to provide a biasing means which will always insure that the damper 26 returns to the normal closed position shown when the air flow through the duct ll ceases. By adjusting the weight 40 along the edge of the latching member 35 in a direction toward the pivot '36 the weight is less effective to bias the damper closed, and conversely as the weight is adjusted downward its effect is greater. Another important factor in the provision of the biasing weight 40 is that as the weight is adjusted toward its lowermost position on the latching member 35, it requires a greater force or pressure of the air flowing in the air duct II to cause a rotative movement of the damper 26 about its pivot 21. The air pressure must therefore be built up to a certain predetermined value depending upon the adjusted position of weight 40 before the damper can be moved.

The latching member 35 is provided with a number of latching positions in which it is restrained and prevented from being moved by either the damper when it responds to the air pressure or by the biasing effect of weight 46. The latching engagements are controlled bya detent member 42 which cooperates in one of its positions as shown with an abutment 43 formed at one end of a circular slot 44 cut in the latching member 35. In this position the detent 42 prevents'any movement of the damper 26 by the flow of air through the duct. Another latching position for the member 35 is provided by an adjustable plate member 45 which is pivoted to pin 36 and adjustably clamped by a screw 46 to the latching member 35. The lower edge of member 45 partially covers the slot 44 and is provided with a latching abutment edg 41 against which the detent 42 is adapted to rest in one of its positions and prevent the return movement of the latching member and therefore the damper 26, when the flow of air through the air duct ceases. In this latching position the damper is held in a partially open position. One end 48 of slot 44 is adapted to engage the detent 42 when the damper is fully open and serves as a stop. A narrow slot 49 formed between the lower edge of adjusting plate 45 and an edge of slot 44 provides a guide passage in the movement of latch member 35 for the detent 42 as it is operated from one latching abutment 43 to the space in slot 44 between the abutments 41 and 48.

The means for operating the detent 42 consists of a slow operating device which preferably comprises a thermostatic or bimetallic element 56 to the free movable end of which the detent 42 is securely riveted as seen in Fig. 2. The other end of bimetal element 50 is fastened by screws to a bracket member 5| which in .turn is'pivoted by a pin 52 to the casing 22. In order to compensate the bimetallic element 50 for changes in ambienttemperature conditions, a

second bimetallic element 53 is provided which is also fastened at one end by screws to the pivoted bracket 5|. The means for causing the operation of the bimetallic element 50 comprises an electric heating element 54 supported upon and in thermal relationship with said element. When the electric heater 54 is energized it causes the bimetallic element 50 to slowly warp its free end carrying the detent 42 in an upward direction as viewed in Fig. 3, and when the heater is de-energized the bimetallic element 50' slowly cools off and warps back to the normal position. During the warping movement of the activebimetallic element 50, the free end of compensating bimetal element 53 is arranged to constantly bear against an adjusting screw 55 which is carried by a bracket 56 supported upon the casing 22. The adjusting screw 55 enables the detent 42 to be accurately positioned with respect to the latched abutments 43 and 41. A coil spring 51 is connected at one end to the bracket 56 and at its other end is connected to the free end of compensating element 53 for maintaining it in engagement with adjusting screw 55. The spring 51 provides an elastic connection between element 53 and screw 55 which prevents binding of the detent 42 in the slot 44 or 49 in case the heater 54 should become disabled at a time while it is energized. In this event the free end of bimetal element 53 would be moved away from its adjusting screw 55 sufficient to release the strain on detent 42 against the edge of slot 44 when the bimetal element 50 is cooled off and thereby permit the latching member to restore and be latched in its normal position as shown. A suitable terminal block 58 for the connection of the internal and external wires of the heater 54 is supported within the casing 22, and a bushing 59 secured to the casing side serves for the 5 entry of the external wires.

In the operation of the device, assume that the stoker motor 8 is operated by the room thermostat l1 calling for heat after an idle or shut down period. The fire bed upon the retort 5 at this'time will be at a very low stage in that its resistance to air flow is low and a preponderance of fine ash exists on the retort. To permit the blower I!) to exert the full blast of air upon the fuel bed at this time would blow the fly ash about as has been pointed out. The motor 8 operates to feed fresh fuel upon the fire bed to effectually cause the fly ash to become fused or smothered while the blower l3 operates to deliver forced combustion air through the air duct H. The full blast of the air flow however is prevented from passing to the retort 8 by the damper 2B which substantially closes the air duct II. The pressure of the air against the damper tends to hold the abutment 43 in latching engagement with the detent 42 through the linkage of arm 32, link 34, and latching member 35, and prevents the opening of the damper. In the latched position of the damper a small amount of air passes around the edges of the damper in the duct so as to gently promote combustion without blowing out the fly ash however. In the closed position the damper also acts as a banking damper to maintain combustion by natural draft during periods when the stoker is not operating. Concurrently with the operation of the stoker motor 8 the electric heater 54 is energized and causes the bimetallic blade 50 to gradually heat up and assume a warped condition at its free end so that the detent 42 slowly moves upward until it disengages itself from latching engagement with abutment 43. The desired timing interval for the unlatching of the detent 42 'is conveniently adjusted by the adjusting screw 55 while manipulation of the rheostat 2| adjusts the amount of heating for the heater 54 so it will not warp the bimetallic element 50 too far and cause the detent 42 to bind against the upper edge of slot 44 when the damper is open. The timing period is arranged so that a suflicient amount of fresh coal is fed to the fuel bed 'so that the disadvantage of blowing fly ash is avoided.

When the detent 42 disengages itself from abutment 43 it passes into the narrow slot 49 and in this position the latching member 35 is free to be moved or axially rotated through the linkage by the action of the air pressure against the damper 26. As a result the damper moves freely to an open position against the force of weight 40 and dependent upon the velocity of the air passing the damper. The velocity pressure is also dependent upon the resistance or porosity of the fuel bed. The weight 40 also provides a certain amount of inertia for preventing a rapid opening of the damper by the air pressure and as a result the damper is opened somewhat gradually which prevents the airflow from being increased instantly to its maximum value too soon.

When the latching member 35 has been shifted to the right hand side for a certain distance by the opening of the damper, the detent 42 rides out of slot 49 and assumes an indefinite position in slot 44 somewhere between abutments 4! and 48. Since the bimetallic element 59 is still being heated by heater 54 the detent continues to be moved upward above the left hand end of slot 49 until it is stopped when the heater reaches its maximum output according to the adjustment ,of rheostat 2|; Accordingly the latching member 35 floats with its abutments 4'3 and 48 positioned somewhere on each side of the detent 42 dependent upon the velocity pressure of the air against the damper 26 and therefore the resistance of its passage through the burning fuel bed.

The fuel and air delivery to the retort continues and the fire bed supplies more heat to the premises being warmed until a. stage is reached wherein the room thermostat ii is satisfied, whereupon it opens its contacts and stops the operation of the stoker motor 8. The stopping of the motor also halts the delivery of forced air by the blower and as a result the damper 25' moves toward its closed position due to its weight and the biasing action of weight 40. The weight 46 is adjusted to be suflicient to cause the linkage 35, 3'4 and 32 to be brought back to normal position carrying the damper alongwith it. The heater 54 being disconnected with the motor, the bimetallic element 53 gradually cools off. The rate of cooling, however, is slow enough so that the detent 42 does not immediately move in register with the slot 49. Instead the abutment 43 engages the detent 4,2 as the latching member moves to the left,- and the damper return movement is halted in a position in which the damper is partially open. The degree of damper opening may be readily adjusted by shifting the plate 45 after loosening the screw '46. The purpose of holding the damper in partially open position for a short time after the'stoker ceases operation is to provide some combustion air to the fuel bed by natural draft through the air duct in orderthat the volatile gasses from the fuel which is fed to the fire bed immediately preceding the stopping of the motor,

' may be burned This delay action also duCeS the tenden y ofhgassesi a d Smoke. om

passing back through the stoker apparatus after the stoker stops. v

After the bimetallic element 50 has cooled sufficiently to move the detent 42 in registry with the slot 49 and out of latching engagement with abutment 41, the latching member 35 is free to rotate back to normal position carrying the damper along with it so that it now assumes its normal closed position. The bimetallic element 50 continues to move the detent downward as it cools off and eventually the detent moves into latching engagement with the abutment 43 as shown in Fig. 3. All elements of the control device are now in normal position and the damper now serves as a banking damper for the fire during the stand-by period.

It will be observed that the time it requires the detent 42 to slide out of latching engagement with the abutment 43 determines the delay period upon the initial delivery of forced air while the fuel is being fed to the fire and prevents the blowing of fly ash, while the time required for the detent to slide out of engagement with the abutment 41 determines the delayed time in which the damper is held partially open to permit the volatile gasses to burn off the fuel. The damper is therefore latched in two different positions for predetermined periods of time, one position at the start of the stoker andanother when the stoker is shut off. The first period of time is primarily influenced by adjusting screw 55, and the.

second period of time is primarily influenced by rheostat 2|.

While the room thermostat I"! operates the stoker whenever there is a call for heat, the interval timer I 8 is effective periodically to cause the operation of the stoker during mild weather when there are relatively infrequent calls for heat, in order that the fire may be maintained alive. Upon a hold-fire operation the stoker in its initial stages functions in the same manner as has been explained, that is, fuelis fed to the retort and air pressure from the fan exerts itself against the closed latched damper as before.

The detent 42 begins to slowly move toward unlatching position with respect to the abutment 43 under control of the heated bimetallic element 50. However, before the detent is unlatched the interval timer 18 causes the stopping of the motor' and the detent moves back. again. The length of time that the timer contacts [9 remain closed is so chosen and anadjustment made that this time interval is relatively shorter than the time required for the bimetallic element 50 to reach a stage in its movement sufficient to unlatch the detent 42 from the abutment '43; 'In

ordinary practice the interval timer contacts l9 are arranged to be closed fora predetermined length of time, depending upon the type of coal being fed to the fire and also the rate of feed; The operation of the stoker under the foregoing conditions enables just sufiicient fresh fuel to be fed to the fire bed to maintain the fire alive until the next operation of the interval timer or until the room thermostat calls for heat. The small amount of air which does pass around the closed damper during hold fire operation and the slight natural draft at other times throughout the furnace is sufiicient to permit combustion of the fuel to take place without loss of the fire. In certain cases it may be desirable to so adjust the relative timing periods between the interval, timer and the bimetallic element 59 that the damper will beopened for a short interval to permit some forced air'to pass to the fire bed before the stoker is shut down. Because no heat is required to heat the premises, the hold-fire period is of just sufiicient length to supply an amount of fuel upon the fire bed to maintain it alive, and therefore it is not necessary to expand the fire to larger heat proportions as would be the case where there is a call for heat. For this reason it is not necessary to open the damper under hold-fire operation.

Without further description it is,thought that the features and advantages of the invention will be readily apparent to those skilled in the art, and it will of course be understood that changes in the form, proportion and minor details of construction may be resorted to, without departing from the spirit of the invention and scope of the appended claims.

What is claimed is:

1. In a fluid control device, a conduit through which fluid is arranged to flow, a valve in said conduit normally biased to closed position in the conduit and movable to open position in response to the flow of fluid through the conduit, a slow operating device actuated with the initial flow of fluid through the conduit, means controlled by said device for preventing movement of the valve to open position upon the initial flow of fluid, and for preventing movement .of the valve to closed position when the fluid flow ceases, said device operating after the lapse of a substantial period of time to cause said means to release the valve for movement'to either of its positions.

2. In an air damper control for an air duct through which air is intermittently delivered, a damper movable in response to the flow of air through the duct and normally biased toward one position, a slow acting device associated with said damper, and means controlled by the actuation of said slow acting device for limiting movement of'the damper in response to air flow upon both the initial flow. of air through the duct and upon the cessation of air flow, said slow acting device releasing said damper for movement in each instance after the lapse of a substantial time interval.

3. In an air damper control for an air duct, a damper movable between closed and open positions in the air duct, stop means including a slow acting device having two operative positions and associated with said damper, said slow acting device in one of its positions preventing the movement of the'dam'per from its closed position, and in its other position preventing the movement of the damper to itsclosed position, said slow acting device operative after a lapsed time interval to release the damper for movement to any of its positions. a I

4. In an air damper control for an air duct through which forced air is delivered, a damper movable to different positions in response to the flow of air through the duct and normally biased to one position when the air vflow ceases, a, slow acting device arranged to preventthe movement of the damper from its biased position upon the intitial flow of air through the duct, said slow device operative to release said damper for movement by the air flow after a'predetermined time delay, said slow device also arranged to prevent the movement of the damper back to its biased position upon the cessation of the air flow in the duct until the lapse of a predetermined time interval, I

5. In an air damper control-for stokers having an air duct through which forced combustion air is delivered whenever the stoker' is operating, a

damper movable to different open positions in the air duct responsive to the flow of air through the air duct, slow operatin means actuated when the stoker is operated, said slow operating means restraining the movement of the damper'by the air flow upon the initial operation of the stoker and operative after a time period to release the damper for movement by the air flow in the duct, means for biasing said damper to closed position in the duct when the flow of air through the air duct ceases after the stoker stops, said slow operating means also restraining the movement of the damper to its biased closed position after the stoker stops and operative after atime period to release the damperfor movement to its biased two different positions, latch means associated with said damper and said slow acting device, said latch means having a different latching engagement in each of the positions of the slow device, one of said latching engagements preventing the movement of the damper from its closed position, and the otherlatching engagement preventing the movement of the damper to its closed position, said slow acting device operative after a time delay period from either of its positions to release the damper from the corresponding latching engagement.

7. In an air damper control for an air duct through which forced air is delivered, a damper normally closing said air duct and moved to open position by the flow of air through the air duct, said damper biased to normal position and being locked from movement in said position, a slow operating device and a latching member having latching engagement therewith, said latching member connected to said damper and movable therewith, said slow operating device operative to release its latching engagement with said latching member after a time interval whereby said damper is free to move-to open position by the air flow through the air duct, means responsive to the cessation of air flow through the duct for moving said damper to its normal closed position and for latching said latch member with the slow operating device, and means connected to said slow operating device to insure the return of the latching member'into latching engagement with said slow operating device in the event the slow operating device should become disabled.

8. In an air damper control for an air duct through which forced air is delivered, a damper arranged to, move between closed and open positions in the duct, a slow operating device oper ated to one position when energized and to another position when ole-energized, a latching member connected to said damper and movable therewith, said latching member having two latching positions with said slow operating device, the energization of said slow operating device being effective to release the latch to permit the damper to move to open position after a time delay period, and the de-energization of the slow operating device being effective to release the latch to permit the damper to move to its closed position after a time delay period.

9. In an air damper control for an air duct through which forced air is delivered, a damper movable between closed and open positions in the duct, a latch member connected to said damper and having a first latching position in which the damper is latched in its closed position and a second latching position in which the damper is latched in open position, and a slow acting device operative when energized to release the latch member from said first latching position to permit the damper to move to open position, and operative when de-energized to release the latch member from said second latching position to permit the damper to move to closed position,

10. In an air damper control for an air duct through which air is delivered, a damper arranged to move between closed and open 'positions in the duct, a latch member connected with said damper, a bimetallic element having an electric heater for causing movement of said bimetallicelement from one position to another, said bimetallic element having latching engagement with said latch member to prevent the movement of the damper until the bimetallic element has moved from one position to the other, and

means for returning the latch member and bimetallic element to latching engagement with each other when the heater is de-energized.

11. In an air damper control for an air duct through which forced air is delivered, a damper in said duct normally biased to closed position and movable to open position by the flow of air through the duct, a latch member connected to said damper and movable thereby,'a bimetallic element having an electric heater for causing movement of the bimetallic element when the heater is energized, said bimetallic element having'a latching engagement with the latch member when the damper is biased closed and the heater de-energized, and another latching engagement when the damper is open and the heater energized, said latching engagements arranged to prevent the movementof the damper from either of its positions until the lapse of a predetermined time interval.

12. In a control for a duct through which fluid passes, a damper controlling the flow of fluid and arranged to move between open and closed positions, first latch means associated with said damper, second latch means cooperating with said first latch means in maintaining said damper in one of its positions, said second latch means upon actuation releasing said first latch means and thereby releasing said damper for movement from said position, and means for actuating said ing said first thermostatic'element for changes in ambient temperature.

14. In a control system for a stoker mechanism having fuel feedingmeans and air feeding means, the combinationof, means responsive to the demand for heat from the stoker mechanism for controlling the operation thereof, a damper for varying the feeding of air, means for causing said damper to assume a relatively open position during normal operation of the stoker mechanism and to move in closing direction to an intermediate position upon stopping of the fuel feeding means, and means including time delay means for causing said damper to move from said intermediate position to substantially closed position a period of time after the fuel feeding means'is stopped.

15. In a control system for a stoker mechanism having fuel feeding means and air feeding means,

' ing of air, said damper means assuming various second latch means including a thermal responsive device mechanically associated therewith, said thermal responsive device including a pair of oppositely acting thermostatic elements exposed to the same ambient temperature, electric heating means for locally heating one of said thermostatic elements, the other of said thermostatic elements compensating the first thermostatic element for changes in ambient temperature.

13. In a control system for a stoker mechanism having fuel feedingmeans and air feeding means, the combination of, means responsive to the demand for heat from the stoker mechanism for controlling the operation thereof, a damper for varying the feeding of air, a thermostatic element mechanically associated with said damper for controlling movement thereof, electric heating means for said thermostatic element and controlled by said responsive means so as to cause said ther mostatic element to change in temperature upon demand for change in operation of the stoker mechanism, and a second thermostatic element subjected to the same ambient temperature as said first thermostatic element and compensatpositions determined by the air pressure for automatically controlling the delivery of the air to the burning fuel, and damper control means including a time delay device for retaining said damper means in at least partially open position for a period of time after the stoker mechanism is placed out of operation. 7

16. In a control system for a stoker mechanism having fuel feeding means and air feeding means, the combination of, means responsive to the demand for heat from the stoker mechanism for controlling the operation thereof, damper means for controlling the feeding of air, time delay means actuated as incidents to starting and stopping of the stoker mechanism for retaining the damper means substantially closed for a'period of time after the stoker mechanism is started and for retaining the damper means at least partially open for a period'of time after stopping of the stoker mechanism, first adjustment means for varyingprimarily said first mentioned period of time, and second adjustment means for vary: mg primarily said second mentioned period of time.

17. In a control system for a stokenme'chanism I having fuel feeding means and air feeding means, the combination of, means responsive to the demand for heat from the stoker mechanism for controlling the operation thereof, a damper for controlling the feeding of air, said damper comprising a blade pivoted 01f center and arranged to assume varying positions corresponding to the action of the air on said blade, adjustable weight biasing means for said blade, damper control means including a thermostatic element for retaining said damper in substantial air flow permitting position for a period of time after the stoker mechanism is placed out of operation, said thermostatic "element having electric heating means therefor influenced by the action of said responsive means.

18. In a control system for a stoker mechanism having a fuel feeding means and air feeding means, the combination of, means responsive to the demand for heat from the stoker mechanism for controlling the operation thereof, a damper for controlling the feeding of air, said damper comprising ablade pivoted off center and arranged to assume varying positions corresponding to the action of the air on said'blade, adjustable weight biasing means for said blade, damper control means including a thermostatic element for holding said damper in substantial air flow restricting position when the stoker mechanism is placed into operation, said thermostatic element having electric heating means therefor influenced by the action of said responsive means and acting a period of time after starting of the stoker mechanism to release said blade for movement determined by the action of the air on said blade and said adjustable Weight biasing means, said damper control means also retaining said blade in substantial air flow permitting position for a period of time after the stoker mechanism is placed out of operation.

19. In a control system for a stoker fired furnace having fuel feeding means and conducting means, pressure responsive damper means associated with said conducting means, said damper means assuming various positions determined by the pressure in a portion of said conducting means for influencing combustion, means responsive to the demand for heat from the furnace for starting and. stopping the stoker, means for causing movement of the damper to a position determined by the air pressure when operation of the stoker is required and for causing movement thereof to draft retarding position when operation of the stoker is not required, and damp er control means operative upon stopping of the stoker to retain the damper means in a draft inducing position for a substantial period of time in order to provide a supply of air to the fire by natural draft for consuming the volatile constituents of green coal supplied to the fire, said damper control means after said substantial period of time permitting movement of the damper means to a draft retarding position.

20. In a control system for a stoker fired furnace having fuel feeding means and conducting means, pressure responsive damper means associated with said conducting means, said damper means including means for causing it to assume various positions determined by pressure in a portion of said conducting means for influencing combustion, means responsive to the demand for heat from the furnace for starting and stopping the stoker, means for causing movementof the damper means from draft retarding position to a position determined by said pressure when operation of the stoker is required and for causing return movement of the damper means to draft retarding position when operation of the stoker is not required, timer means for controlling the damper means and having a first position which prevents movement of the damper means to draft retarding position, said timer means moving from said first position to a second position a substantial period of time after stopping of the stoker, the timer means upon movement to said second position permitting movement of the damper means to draft retarding position.

HOMER E. MALONE. 

